Chlorine cell having protected diaphragm



July 12, 1960 R. D. BLUE ETAL 2,944,956

CHLORINE om. HAVING PROTECTED DIAPHRAGM Filed Nov. 16, 1956 2 Sheets-Sheetl 1 Fl TTORNEKS July 12, 1960 R. D. BLUE ErAL CHLORINE .CELL HAVING PROTECTED DIAPHRAGM 2 Sheets-Sheet 2 Filed Nov. 16, 1956 QMS:

6e// Vo/fage set up local electrolytic side reaction y formation 'of alkali carbonate in the cell eiuent and C O in the chlorine gas bythe 'electrolysis of the alkalihydroxide in the diaphragm. In the practice of the invention, we prefer to fabricate the structural material into an interwoven orgmeshed configuration and thereafter treat said materialwith an aqueous dispersion of the polymer as by a dipping, spray'V ing or brushing application and thereafter cure in accordance with the recommended procedure for such polymer.

As an alternative to the preferred practice of the invention, the individual untreated fibers may be treated with the polymer and cured prior to fabrication and` cured, and positioned in the cell in accordance with the invention. v y

.The annexed drawing shows one form of the cell of the invention. Y. Fig.v 1 of the drawing isa -side elevational view, taken on line 1-1 of Fig. 2, in section.

Fig. `2'. is an enlarged horizontal Fig. l on line 2-2 of Fig. 1.

Fig. 3 is an enlarged fragmentary portionof the cathode assembly of Fig. 2.

s resulting "in `the i Inlet pipe 13 in bottom 20 provides for the ingress of an aqueous solution of an' alkali chloride,- referred to hereinafter as brine, into anolyte compartment 6. Out-L let 14 in top 21 provides for an escape of chlorine gas evolving at the anode. In plate 26 is pipe 1.5 for egress of the alkali hydroxide and outlet 16 for escape of hy# drogen gas and other gases, if any, from catholyte compartment 7. Strainer 17, positioned in pipe 13 at its j' entrance to anolyte compartment 6, retains the particles Fig. 4 is an elevational View of the novel protective 3;,

screen of the cell of Fig. 1. Y Fig. 5 is a section of the protective screenon line S--S of Figure 4 showing one fold of the screen.

Figs. 6 and 7 are graphs which show voltages required in the cell employing the novel features of the Vinvention in comparison to voltages required by cells which' do not employ such novel features but are otherwise comparable. The effect on voltage consumption brought about by washing both types of cell is also shown.

- Referring to the drawing in more detail, there is shown a cell of the invention having concrete body structure 1,"

phragm 5 on the anode side thereof is novel protective..- coated vgrating or screenk8. Asbestos diaphragm 5 isi thereby positioned between cathode 2 and screen' 8. Cov,-l ering the opening in wall 23, as defined by wall Aedge 32., is plate 26. Plate 26 has ridge-33 thereon whilchfollows the general outline of Wall edge 32 and which lis raised inwardly toward border 34 of cathode 2; Studs 30 secure; plate 26 to V'wall 23 and also hold ridge'33` of plate 246 in rm contact with border 34'of cathode 2. To plate f' Z6 is attached terminal 3 which in turn makes Contact" with negative lead-in line 4 attached to a source of direct current. Plate 26, therefore, serves as Aboth the 'outer inclosing wall of catholyte compartment 7 and a bus 'barf for carrying negative electricity to cathode 2..V

In contact with `screen 8 is anode graphite particle! 65 body 9 which is loosely compacted in'anolyte compartment 6.' Weight 28 maintains a compacting effect onv particle body 9.

Graphite block-10 is inserted in the' of graphite in compartment 6 and yet permits entrance of fresh brine thereto through pipe 13. Gasket 18 provides a'snug fit between outlet 14 and the opening provided therefor in top 21. Gasket 19 provides a snug t between the plate 26 and wall 23 about the opening defined by wall 32.

The novel grating or screen 8 shown in the drawing was made by cross-Weaving JAG inch asbestos cord at about 5%; inch center-to-center spacing and thereafter dipping the uncoated grating for about 5 seconds at room temperature, into about a 40 percent aqueous colloidal dispersion or suspensoid of polytetrafluoroethylene, eg., Teflon latex. The coated grating was dried overnight at room temperature and thenv baked at 350 C. for about setio of the cell of; l' 15 minutes. It was then placed in position in the cell as shown in the drawing.

. The anolyte compartment between anode block 10 and grating 8 was about 3A inch in width where the folds of the cathode extend -farthest toward block 10, i.e., at the narrowest width. The space thus formed was packed with graphite pieces which were generally spheroidal and about 1/2 to 956 inch in diameter.

, To operate the cell of the invention, a brine consisting '-1 essentially of aconcentrated salt solution, for example,

about 315 grams of sodium chloride per liter of water,- is pumped into anolyte compartment 6 through inlet 13. The electrolysis of the brine is started by setting up an electrical potential between anode particle body 9 and i; cathode 2 by attaching lead-in line 12 to the positive take-olf of a D.C. source of electricity (not shown) and lead-in line 4 to the corresponding negative take-off of the same source of electricity. The brine is permitted to rise in anolyte compartment 6 until it is above the graphite Y particle body 9, when the brine ilow is cut back so as to maintain level 29 above graphite particle body 9 and below that which would result in an overow out through outlet 14.

The brine comes into contact with the anode comprising block 10 and particle body 9, but especially with the particles of graphite body 9 forming chlorine, and cathode 2, forming ultimately sodium hydroxide and hydrogen gas. The chlorine, thus formed, rises and passes out through outlet 14. The alkali hydroxide, referred to as the caustic, e.g., sodium hydroxide, thus formed, together with water from the brine and some undecomposed salt,

flows to the bottom of the Vcatholyte compartment 7 and passes out through outlet'lS. The hydrogen rises and passes out through outlet 16. Asbestos diaphragm 5,

t since contact with particle `body 9 is prevented by novel screen 8, prevents intermingling of products formed in the anolyte compartment with those formed in the catholyte compartment.

Diaphragm 5 in conjunction with novel screen 8 pre- Y vents both the combining of chlorine and hydrogen, which opening provided therefor in wall 22. Graphite block 10 forms both outer wall of anolyte compartment '6 and a portion of the anode of the cell. Perpendicula'r to block 10 arehorizontal extensions 27`which, together with block 10,@ insure goodelectrical contact with the body of graphite particles L9. Terminal 11 is secured ,to--

anode Yblock 10 by meansof contact bar 31` andinasposi-V in the absence of separatory means often takes place with explosive violence, and prevents the reaction between alkali hydroxide and chlorine, which would result in the formation of the hypochlorite and later the chlorate. The

i chlorate, if formed, would attack the carbon of the anode vention.

By referring toFigures 6 and 7 of the drawing, the

decreased voltage A. requirement ,for .cells c constructed:

according to the invention may be compared to cells which are presently in use. The broken lines represent voltages used by cells a and b which are of conventional construction; the solid lines represent voltages used by cells a and b' which employ the novel features of the invention. Vertical lines designated wash represent washings of the asbestos diaphragm which were done after the number of days of continuous operation shown on the horizontal axis. The voltage required to operate the four cells are set out on the vertical axis and the days of continuous operation are set out on the horizontal axis of Figures 6 and 7.

The cells a and a', the performance of which is shown in Figure 6,- employed asbestos diaphragms formed by wet asbestos being drawn against the cathode screen before assembling the cells according to known practice and as described hereinabove. Cells b and b', the performance of which is shown in Figure 7, employed asbestos paper of a thickness of about 0.05 inch according to known practice. Except for the novel features of the invention in cells a and b' and the employment of drawn asbestos diaphragms in cells a and a and paper asbestos diaphragms in cells b and b the cells were of the same construction. The graphs show a reduced voltage consumption of 0.1 to 0.2 volt when the novel cell of the invention was used. Such reduced voltage substantially reduces the kilowatt hours of power consumed on a large scale operation and is of appreciable economic importance.

Additional advantages of the cells constructed according to the invention -are present which are not apparent from examination of Figures 6 and 7. Among such advantages is the lower cost of graphite for the anode. In conventional cells, single graphite blocks or shapes are used. Therefore, in conventional cell operation, physical erosion and chemical reaction of the blocks occur which widen the spacing between anode and cathode, thereby increasing the cell resistance after protracted operation. In cells constructed according to the invention, graphite erosion and consumption are largely conined to the pieces which may be spheroidal, rod-shaped, or generally irregular in the nature of the particles forming body 9 of the drawing. Therefore, a spacing between the anode and cathode which is not substantially greater than the thickness of the diaphragm and the novel screen can be maintained for long periods of operation. Another advantage is that additional particles are readily added without dismantling the cell. Furthermore, the graphite particles are procurable at lower cost than are single speciiically shaped graphite of relatively large size.

A further advantage to be derived from the practice of the invention is yfound by determining the percentage of carbon dioxide in the chlorine gas evolving from the anolyte compartment. In a conventionally constructed cell, the percentage of carbon dioxide was found to be in the range of 1.0 to 1.5 percent. In contrast thereto, the percentage of ca-rbon dioxide was as low as 0.2 percent in the chlorine evolving from `a cell which employed graphite particles in the anode and which contained the protective screen of the invention described hereinabove, but which was otherwise of comparable construction to a conventional cell.

It is understood that cells containing protective gratings or screens which are but modications of the screen here in illustrated are Within the teachings and scope of the invention. For example, a cell containing a protective grating composed of strands of metal, glass, or natural or synthetic bers which are woven so as to permit permeation of brine for electrolysis between the strands, and which are coated, dipped, or otherwise impregnated with non-conducting, non-reactive polymer such as a polymerized halide-substituted ethylene, e.g., polytritluorochloroethylene (polymonochlorotriuoroethylene) as described in U.S. Patent 2,686,738 or polytetrailuoroethylene as described in U.S. Patent 2,710,266 are within the scope of the invention. The preparation of a polymerized halide-substituted ethylene coating according to one of the above cited patents is only a suggested method. 'I'he polymer useful in the present invention is in norway limited by its method of preparation and may be prepared according to any method so long as the polymer produced is suiciently structurally re-inforcing and is electrically non-conducting, and is non-reactive with the fluid ingredients of the cell.

Having described the invention, what is claimed and desired to be protected by Letters Patent is:

1. In an improved diaphragm-type chlorine cell for the electrolytic decomposition of a chloride brine in the production of chlorine gas containing a non-conducting diaphragm which has small resistance against distortion, perforation, and dislodgement from position and which divides the cell into an anolytc compartment and a catholyte compartment, the improvement comprising a substantially rigid screen composed of meshed filaments positioned parallel to and adjacent to said diaphragm for the protection of the diaphragm on the lanode side thereof, the laments of said screen being coated with a protective coating selected from the group consisting of polymerized monochlorotriuoroethylene and tetrauoroethylene, and an anode consisting of a body of particulate graphite of a minimum particle dimension greater than that of the meshes in said screen compacted in said anolyte compartment land resting against said screen, and a rigid graphite core adapted to be attached to a source of electrical energy extending into said body of particulate graphite.

2. An improved cell for electrolysis of brine comprising a cell chamber; a metal cathode within said chamber having openings therein for the passage of uids therethrough; -a uid-permeable electrically non-conductive diaphragm which is easily distorted, perforated, and dislodged from position by contact with hard solid fragmented objects located adjacent to said cathode and dividing said chamber into a catholyte compartment and an anolyte compartment; a structurally self-supporting substantially rigid perforate sheet of polymer selected from the group consisting of polytetrafiuoroethylene and polymonochlorotriuoroethylene positioned substantially parallel to and adjacent to said diaphragm in the anolyte compartment; and an anode comprising a compact body of fragmented carbon selected from the group consisting of amorphous carbon and graphitized carbon in contact with said protective sheet, said fragmented carbon being of greater size than the perforations in said protective sheet and a rigid continuous electrically-conductive member in contact with the body of fragmented carbon.

References Cited in the le of this patent UNITED STATES PATENTS 498,771 Craney June 6, 1893 522,618 Roberts .Tuly 10, 1894 885,998 Hirtz Apr. 28, 1908 1,239,443 Antisell Sept. 11, 1917 1,309,148 Michel July 8, 1919 2,330,404 Burns et al. Sept. 28, 1943 2,532,629 Konrad etal. Dec. 5, 1950 FOREIGN PATENTS 633,541 Great Britain Dec. 19, 1949 1,123,583 France `Tune 11, 1956 OTHER REFERENCES Yelton: Transactionsof the Electrochemical Society, .VOL (1946), pp. 331 to 339. 

1. IN AN IMPROVED DIAPHRAGM-TYPE CHLORINE CELL FOR THE ELECTROLYTIC DECOMPOSITION OF A CHLORIDE BRINE IN THE PRODUCTION OF CHLORINE GAS CONTAINING A NON-CONDUCTING DIAPHRAGM WHICH HAS SMALL RESISTANCE AGAINST DISTORTION, PERFORATION, AND DISLODGEMENT FROM POSITION AND WHICH DIVIDES THE CELL INTO AN ANOLYTE COMPARTMENT AND A CHOLYTE COMPARTMENT, THE IMPROVEMENT COMPRISING A SUBSTANTIALLY RIGID SCREEN COMPOSED OF MESHED FILAMENTS POSITIONED PARALLEL TO AND ADJACENT TO SAID DIAPHRAGM FOR THE PROTECHTION OF THE DIAPHRAGM ON THE ANODE SIDE THEREOF, THE FILAMENTS OF SAID SCREEN BEING COATED WITH A PROTECTIVE COATING SELECTED FROM THE GROUP CONSISTING OF POLYMERIZED MONOCHLOROTRIFLUOROETHYLENE AND TETRAFLUOROETHYLENE, AND AN ANODE CONSISTING OF A BODY OF PARTICULATE GRAPHITE OF MINIMUM PARTICLE DIMENSION GREATER THAN THAT OF THE MESHES IN SAID SCREEN COMPACTED IN SAID ANOLYTE COM- 